Any large park in a big city gets my vote even if it is a housing estate for the homeless and a garbage dump based on the vagaries of the wind.
Most of Papago Park is a delightful expanse if well-used bike and walking paths. Most people are here to visit either the Phoenix Zoo or the Desert Botanical Gardens but there are a number of other places you can visit while you are in the area.
Last time I was here I watched a coyote run across one of the hills less than 50 yards in front of me. There is an abundance of jackrabbits running helter skelter all around you if you look carefully.
There are a number of hills and valleys to negotiate as well as many different rock formations to explore. There is usually enough parking close to where you want to be although some of the parking lots fill to capacity early in the morning before the sun is burning.
Enjoy the park!